Migration

SPECIES FOCUS:
| Species Focus |
PINK-FOOTED
GOOSE
indoor environment, but were able to view the night sky.
And remarkably, at the time of the year when they would
normally migrate, they began becoming restless, and
actually oriented themselves in the direction they would
naturally travel during migration. The scientists called this
phenomenon Zugunruhe, from the German words for
restlessness and migration.
So what triggered this remarkable behaviour? It’s due to a
cluster of light-sensitive cells on the forehead of birds, a
throwback to a more complex organ present in the first
vertebrates, which functioned as a ‘third eye’. In most
mammals it’s become a vestigial organ, but in birds
this organ is developed enough to detect changes in
patterns of daylight. How do these cells react? By
sending chemical signals to the pineal gland, the
part of the brain that controls the sleep-inducing
hormone melatonin, telling it to increase levels of
melatonin secreted.
which stimulates birds to eat more, building up fat
reserves for the flight.
Image: Edward Grierson
Once again, winter is withdrawing its hold, and the
British countryside is beginning to turn green.
Snowdrops, the first flowers of the year, are already
popping up in the garden, and the cherry trees are beginning
to blossom. Spring is well on its way.
Naturally, this means that the birds that stayed here for
winter are packing their bags, and on their way back to
their breeding ground. For several months, our farm has
hosted German blackbirds, Danish goldcrests, Norwegian
fieldfares and Icelandic whooper swans.
But there is one bird that outstrips them all, in number,
travelling distance and its significance to me. And that bird
is the pink-footed goose. Every Autumn some 15,000 of
them fly all the way from Greenland to my neck of the
woods-lowland Perthshire- to escape Arctic winters. The
sound of a 30-strong gaggle on a clear December evening
is a true spectacle for the ears. But now, having built up
weight over the winter thanks to the unintended efforts of
farmers like us, they’re beginning to head off, and gaggles
Edward Grierson tells us about these
masters of migration.
flying north have become a regular sight.
All well and good, but this is a Herculean journey they’re
undertaking. It involves a flight of 2,400km, including
crossing hundreds of kilometres over open sea with
nowhere to land. And they have no sat-nav, OS Map or
compass. So how do they do it?
Well, we don’t have all the answers on this subject, but do
we know of several remarkable adaptations in pink-footed
geese that allow them to pull off this feat.
The problems faced by migratory birds are two-fold: timing
and navigation. First of all, timing. How do they know
when to migrate, and how do they prepare themselves for
the long journey?
Well, in the 1950s, a team of German scientists began
an experiment involving whitethroats and blackcapsboth
species are also British migrants, though unlike
geese they arrive for the summer. They were placed in an
Images: Copyright North East Wildlife: www.northeastwildlife.co.uk
The consequence of this is that the body clocks of the birds,
such as our geese, are altered, causing increased restlessness.
The alteration of their sleeping patterns allows them to
cross multiple time zones without succumbing to jetlag,
and keeps them on the wing for extended periods of time
when flying over open seas. There are also some studies that
suggest the pineal gland increases the release of prolactin,
But this leads to the second problem the geese face when
migrating: navigating. How do they know which way
to go to get to their summer grounds? As a matter of
fact, geese use several methods.
One is reading the stars. While the constellations
change their position in the night sky throughout
the year, one star is always aligned to the North Poleit
is, of course, the Pole Star. So if a goose wishes to
fly to Greenland from Scotland, it uses the Pole Star to
find which way is North, and orients itself based on this
(birds migrating south navigate by following the South
Star, which is aligned to the South Pole). And geese have
another trick: their beaks contain small traces of ferrous
iron, a magnetic metal. This allows them to read Earth’s
magnetic field, using their beaks as built-in compasses to
direct them to their breeding grounds.
So that’s how the pink-footed goose carries out such a
feat. And just this morning, there was yet another gaggle
flying over our roof. I wish them all the best of luck, and
a pleasant journey.
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